Just my opinion, but cryptopia is the best exchange that i have ever used only because they are 100% descentralized and they will never ask you for ID's.
I just started trading and the very first problem i encountered is what trading site shall i use?
my friends from gambling site suggested some and i decided to pick cryptopia
Poloniex is good too (just like you said) but it is going to ask for ID's soon and that is something that you should be afraid of if you have funds in there.
And whatever you do, do not use bittrex.